The present application is a continuation-in-part application No. PCT/JP00/01950 filed on Mar. 29, 2000, designating U.S.A and now pending.
1. Field of the Invention
The present invention relates to a multilayer antireflection film, an optical member, and a reduction projection exposure apparatus and, more particularly, to a multilayer antireflection film for oblique incidence, which is effective to s-polarized light of the wavelength of not more than 250 nm such as excimer laser light or the like, an optical member provided with the multilayer antireflection film, and a reduction projection exposure apparatus provided with the optical member.
2. Related Background Art
Lasers such as excimer lasers and the like have been developed as light sources of ultraviolet light in recent years and, in conjunction therewith, the lasers have been being used in optical devices making use of the ultraviolet light. For various purposes, the optical members used in optical systems of these devices need to be able to be used with light undergoing oblique incidence and the antireflection film for the optical members must have the antireflection effect against the light undergoing oblique incidence.
The excimer laser light is generally linearly polarized light and whether it is incident as p-polarized light or as s-polarized light to the optical member is dependent upon placement of the optical member in the optical system. Specifically, the incident light is the p-polarized light when it is in such a positional relation that the electric field vector of the wave of incident light vibrates in parallel to the plane of incidence to the optical member, but the s-polarized light when it is in such a positional relation that the electric field vector vibrates normally to the plane of incidence to the optical member.
Japanese Patent Application Laid-Open No. HEI 10-268106 discloses the technology of the multilayer antireflection film for oblique incidence and describes that, where the incident light is the p-polarized light, the antireflection films of 5-layer, 7-layer, and 9-layer structures have the antireflection effect for the p-polarized light incident at angles of incidence xcex8=70xc2x0, 72xc2x0, and 74xc2x0, respectively. An angle of incidence means an angle between a normal to a surface of a substrate and incident light.
By placing the optical member so that the light incident to the antireflection film formed on the optical member is the p-polarized light as described above, reflection of light can be reduced at the surface of the optical member.
The conventional antireflection films, however, were those effective only to the p-polarized light and, in order to place the optical members such as lenses, mirrors, prisms, and so on in the optical systems etc. of the, reduction projection exposure apparatus, consideration must be given to such arrangement that the light is incident as the p-polarized light to all the optical members. This decreased degrees of freedom in designing of the apparatus and constituted a restriction on optimization of performance and compactification of the apparatus.
The present invention has been accomplished in view of the issue in the above-stated conventional technology and an object of the present invention is to provide a multilayer antireflection film for oblique incidence that has the excellent antireflection effect for the s-polarized light of the wavelength of not more than 250 nm, such as the excimer laser light or the like, and that is effective in improving the performance such as imaging performance and the like of reduction projection exposure apparatus, an optical member, and a reduction projection exposure apparatus.
The inventors have been conducted intensive and extensive studies in order to achieve the above object and, as a result of the studies, found out that the above issue was solved by a multilayer antireflection film provided with a specific laminate, an optical member provided with the antireflection film, and a reduction projection exposure apparatus provided with the optical member, thus accomplishing the present invention.
Namely, a multilayer antireflection film of the present invention comprises:
a laminate consisting of an alternate stack of at least one low-refractive-index layer and at least one high-refractive-index layer, wherein at least one of outermost layers in the laminate is a low-refractive-index layer, and the multilayer antireflection film having the antireflection effect for s-polarized light of a specific wavelength of not more than 250 nm incident to the low-refractive-index layer.
An optical member of the present invention comprises:
a substrate capable of transmitting s-polarized light of a specific wavelength of not more than 250 nm; and
a multilayer antireflection film comprising a laminate placed on the substrate and consisting of an alternate stack of at least one low-refractive-index layer and at least one high-refractive-index layer, wherein at least a layer on the far side from the substrate out of outermost layers in the laminate is a low-refractive-index layer, and the multilayer antireflection film having the antireflection effect for the s-polarized light of the specific wavelength of not more than 250 nm incident to the low-refractive-index layer.
Further, a reduction projection exposure apparatus of the present invention is a reduction projection exposure apparatus comprising:
an exposure light source, a photomask on which a pattern original image is formed, an illumination optical system for illuminating the photomask with light emitted from the light source, a projection optical system for projecting a pattern image emerging from the photomask, onto a photosensitive substrate, and an alignment system for alignment between the photomask and the photosensitive substrate,
wherein at least one of optical members constituting the light source, illumination optical system, and projection optical system is an optical member comprising:
a substrate capable of transmitting s-polarized light of a specific wavelength of not more than 250 nm; and
a multilayer antireflection film comprising a laminate placed on the substrate and consisting of an alternate stack of at least one low-refractive-index layer and at least one high-refractive-index layer, wherein at least a layer on the far side from the substrate out of outermost layers in the laminate is a low-refractive-index layer, and the multilayer antireflection film having the antireflection effect for the s-polarized light of the specific wavelength of not more than 250 nm incident to the low-refractive-index layer.
According to the present invention, the laminate of the multilayer antireflection film is the alternate stack of at least one low-refractive-index layer and at least one high-refractive-index layer and at least one of the outermost layers is the low-refractive-index layer, whereby the reflectance is reduced where the s-polarized light of the wavelength of not more than 250 nm is obliquely incident to the low-refractive-index layer of the antireflection film. When the reduction projection exposure apparatus is constructed using the optical member provided with the multilayer antireflection film in such arrangement that the outermost layer on the far side from the substrate is the low-refractive-index layer, degrees of freedom in designing of the apparatus increase, so as to allow the optimization of performance and the compactification and it becomes feasible to attain excellent imaging performance, which has never been accomplished by the conventional devices, accordingly.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.